The Washington Post has released its annual list of the nation’s most challenging high schools — and Idaho’s honor roll is unchanged from 2016.

Nine Idaho schools made the list, which is based on what the Post’s Jay Matthews calls “an index formula that’s a simple ratio.” Matthews divides the number of Advanced Placement, International Baccalaureate and Advanced International Certificate of Education tests given per graduating senior. The higher the ratio, the higher the ranking.

Here’s the Idaho list, with national rankings in parentheses:.

• Riverstone International School, Boise (116).
• North Star Charter School, Eagle (164).
• Coeur d’Alene Charter Academy (466).
• Boise High School (594).
• Timberline High School, Boise (776).
• Borah High School, Boise (1,249).
• Capital High School, Boise (1,359).
• Century High School, Pocatello (1,977).
• Vallivue High School, Caldwell (2,029).

The same nine Idaho high schools made Matthews’ 2016 list.

At Riverstone, a private school, exactly six college-level tests were administered per student, and every graduate passed at least one such test.

At North Star, one of two charter high schools on the list, 95 percent of graduates passed at least one college-level test. The Coeur d’Alene Charter Academy had a 78 percent passage rate.

The rankings are not weighted based on student demographics, but the Idaho rankings are heavily skewed toward schools with low poverty rates. At Riverstone and North Star, no students qualify for free or reduced-price lunch. And six of the nine schools on the Idaho list have poverty rates well below the state’s average; the lone exceptions are Borah, Capital and Vallivue.